Downdraft ventilation hood



FIG. 1 is a front view of a downdraft ventilation hood showing my ornamental design, those surfaces which are hidden are the same as those which are illustrated by the other figures;

FIG. 2 is a top view thereof;

FIG. 3 is an enlarged left view thereof; and,

FIG. 4 is an enlarged right view thereof. 

The ornamental design for a downdraft ventilation hood, as shown and described. 